Process of preparing 3-amino-2-cyano acrylamide

ABSTRACT

This invention relates to a new use of intermediates and an improved method of preparing amino methylene cyano-acetamide by reacting formamidine base with cyano-acetamide. In addition this invention is directed to reacting amino methylene cyano-acetamide with hydrazine to form 3-amino pyrazole-4-carboxamide which may then be converted to Allopurinol. Allopurinol is a drug useful in the treatment of hyperuricemia.

United States Patent Cresswell et a1.

[ PROCESS OF PREPARING 3-AMINO-2- CYANO ACRYLAMIDE [72] Inventors: Ronald M. Cresswell, 34 Walbrooke Road, Scarsdale, NY. 10583; Melvin Schnapper, 41 Homecrest Oval, Yonkers, NY. 10703 [22] Filed: Sept. 9, 1969 [2]] Appl. No.: 856,488

Related US. Application Data [63] Continuation-impart of Ser. No. 651,393, July 6, 1967, Pat. No. 3,487,083.

[52] US. Cl ..260/465.4, 260/256.4 F, 260/310 R,

424/251 [51] Int. Cl ..C07c 121/30 [58] Field of Search ..260/465.4, 310 R [56] References Cited UNITED STATES PATENTS 2,998,425 8/1961 Dickinson et al. .....260/310 R 3,121,108 2/1964 Josey et a1 ..260/310R FOREIGN PATENTS OR APPLICATIONS 695,522 10/1964 Canada ..260/310 R [451 Sept. 26, 1972 854,632 11/1960 Great Britain ..260/31OR OTHER PUBLICATIONS Huffman et al. J. Org. Chem., Vol. 27, Pages 551- 558, (1962). OD241J6 Kenner et al. J. Chem. Soc., (London) 1943, Pages 388- 390. QD1.C6

Smolin et a1. S-Triazines, Pages 9- 13, NY, Interscience, 1959. QD401.S62

Primary ExaminerNata1ie Trousof AttorneySewall P. Bronstein and Donald Brown 5 7] ABSTRACT 5 Claims, No Drawings PROCESS OF PREPARING 3-AMINO-2-CYANO ACRYLAMIDE This application is a continuation-in-part of U.S. Pat. Application Ser. No. 651,393, filed July 6, 1967, now US. Pat. No. 3,487,083.

This invention related to a new use of particular intermediates and an improved method of preparing intermediates, useful in the preparation of Allopurinol (4-hydroxypyrazolo [3,4-d] pyrimidine).

Allopurinol is a drug useful in the treatment of 10 hyperuricemia in humans associated with gout and other conditions. Allopurinol is also useful in inhibiting the enzymatic oxidation of mercaptopurine and other purine drugs.

Allopurinol is generally administered to human patients in tablet form. Dosages of 200 to 300 mg. per day divided into two or three, doses is recommended for treatment of mild gout and dosages of 400 to 600 mg. per day is recommended for treatment of those having moderately severe tophaceous gout.

The compound 4-hydroxypyrazolo [3,4c-d] pyrimidine (Formula I) l p K,

H (I) has previously been prepared by preparing ethoxy methylene malononitrile 11 ON C2H5OCH=C/ ON (II) which was reacted with hydrazine III H2HNH2 (III) to Form IV (see U.S. Pat. No. 2, 759, 949).

NC-(i H N- Z \N/ (IV) The compound (IV) is then hydrolyzed to form 3- amino pyrazoloi-earboxamide (V).

o HzN-( \r HN- N/ II (V) The compound V is then reacted with formamide (VI) NH; cg;

to prepare the compound I.

The prior art has also disclosed an alternate method of preparing Allopurinol (I) which comprises reacting ethoxy methylene cyano-ace'tic ester (VII) C2II5O(HJ :ouoom N (VII) with hydrazine III to produce VIII 2 E cnnopl:

inN N/ which is then reacted with formamide (VI) to provide I.

The above mentioned prior art methods have been used to produce Allopurinol. The Allopurinol so produced by the prior art has been contaminated with various pyridine derivatives etc. which are rather insoluble and which tend to be yellow in color. Their presence is readily detectable through their absorption spectrums (U.V. and Visible).

Since Allopurinol is a drug which is continuously used by chronically ill patients, objectionable side products can not be tolerated. These side products must be removed by using costly and tedious procedures in order to provide a drug product which is acceptable for distribution.

In view of the above, it is the principal object of this invention to provide new and improved methods for preparing intermediates necessary For the preparation of Allopurinol in a highly pure state such that little or no purification of the intermediates and/or of the end product is necessary.

This invention provides the carboxamide (V) intermediate in high yield percent) and in high purity without any necessary isolation of intermediates during further processing. None of the prior art methods offer these advantages.

The new process of this invention comprises two steps, A and B, which can, in fact, be telescoped into one continuous operation. Step A comprises reacting the known formamidine base IX (VIII) I IH (IX) with the known cyanoacetamide X GEN NHz (X) to produce 3-amino-2-cyan0 acrylamide XI ON CIT-=4 NlIz N112 (X The B-amino-a-cyano acrylamide of formula XI has been prepared before by other types of reactions. However, the present reaction is remarkable as proceeding rapidly at or even below room temperature (preferably at 5 to less than about 30 C.). The formamidine and cyanoacetamide may be mixed together in at least about equal molecular amounts in the above step A. It is possible that the mechanism is:

11m CN Hm ON on 111? (111 61 1 ILIH ooNm +I IHz CONHz HzN CN \CHCH Nfi. CONH:

CN HzN-OH=( iCONH2 The basicity of formamidine and the acidity of cyanoacetamide are consistent with the presence concurrently of working concentrations of the cation of the former and the anion of the latter. The speed and smoothness of the reaction is such as to suggest an ionic process since it appears to have a very low energy of activation.

The solvent for this step can be water or a lower alcohol, or obviously a combination of both, i.e., methanol, ethanol, propanol, butanol. The reaction is slightly faster in water and indeed is appreciably exothermic at room temperature. However, the product obtained in alcohol is preferably for our purpose and consequently it is preferred to run the reaction in alcohol.

The prior art has disclosed the use of s-triazine and cyanoacetamide to produce 3-amino-2-cyanoacrylamide, but the reaction proceeds such that the following competing reaction occurs:

C ONH2 16TH C ONH: CONHQ (EH3 (llH :CH-NH: CH2 CN NHg CN H I? C ONH: C ONH2 HzNC ON I I HQN O H ON N The products of these side reactions are extremely difficult to remove whereas in the case of the method of this invention, the use of fonnamidine base does not produce the above side products and furthermore does not produce thru any side products which are difficult to remove.

Step B consists of reaction of the amino cyano acrylamide (XI) formed in Step A with hydrazine (III) to produce 3-amino pyrazole-4-carboxamide (V). A salt of V is generally prepared by adding an acid solution to produce the salt. Mineral acids such as sulphuric, hydrochloric etc. may be used with sulphuric acid and the sulphate salt prepared therefrom being preferred.

This step can be performed on the isolated aminocyano acrylamide or the two steps can be combined operation which, in practice, is preferred. The separate steps A and B are described in Examples 1 and 2; Example 3 describes the combined operation. l-lydrazine is added to the reaction mixture which is warmed at a temperature in the range of 100 C. Thereafter the compound Allopurinol (I) can be prepared by reacting (V) or a salt thereof with formamide (VI). Example 4 illustrates the preparation of 4-hydroxy pyrazolo pyrimidine from a salt of V.

It should be understood that it is unnecessary to isolate the amino cyano acrylamide XI with this invention. Cyclization to Allopurinol can be effected by heating with formic acid or formamide alone or with the two in combination which is a faster and the preferred route.

All temperatures given in the examples are in degrees centigrade.

EXAMPLE 1 3-Amino-2-cyano acrylamide To a solution of sodium methylate (5.94 grams) .1 l m in ethanol 50 ml.) was added formamidine hydrochloride (10.0 grams) 0.125 m preferably in a slight excess and the mixture was stirred at room temperature for 15 minutes. The mixture was then filtered free of salt.

To the filtrate was added cyanoacetamide (8.4 grams) 0.1 m and the reaction mixture was stirred at room temperature for 1 hour. The 3-amino-2-cyanoacrylamide that separated was collected and washed with ethanol (25 ml) Weight 7.6 grams. The Filtrate on cooling to 5 C. yielded a further 1 gram of product. Total weight 8.6 grams (77.5 percent) m.p. 185 186 C. lit m.p. 1823 C.

EXAMPLE 2 To a suspension of 3-amino-2-cyano acrylamide (24.5 grams) in water (100 ml.) was added 85 percent technical hydrazine hydrate (13 grams) and the stirred mixture was heated rapidly to 7080 on a steam bath. The reaction was held at that temperature for 15 minutes and then allowed to cool to 25C. At 25C. the reaction was was acidified by the addition of a solution made from concentrated sulphuric acid (20 ml.) and ice (50 grams). The acidified reaction was cooled to 5 C. and the product collected and recrystallized from water (350 ml.) with charcoal (3.3 grams) treatment. The white crystalline 3-amino pyrazole-4-carboxamide sulphate was collected and washed with water (2 X 50 ml.; 5C.), acetone (2 X 100 ml.) and dried in vacuo at 60 C. Weight 28 grams; Yield 72.5 percent m.p. 229232 (decomp.)

EXAMPLE 3 3-Amino pyrazole-4-carboxamide sulphate To a solution of sodium methylate (6 grams) in ethanol ml.) was added formamidine hydrochloride (10 grams) followed immediately by cyanoacetamide (8.4 grams). The reaction was stirred at 25 C. for 3 hours and then heated to 70. At 70 a solution of percent technical hydrazine hydrate (6 grams) in water (50 ml.) was added and after a further 15 minutes at 70 C. the reaction mixture was allowed to cool to 25 C. At 25 C. the reaction was acidified by the addition of a solution made from concentrated sulphuric acid (6 ml.) and on ice (30 grams). The acidified reaction mixture was cooled to 5 C. and the crystalline product collected and recrystallized from water (175 ml.) with charcoal treatment. The white crystalline 3-amino pyrazole-4-carboxamide sulphate was collected and washed with water (50 ml.; 5 C.) and acetone (2 X 50 ml.) and dried in vacuo at 60 C.

EXAMPLE 4 4-Hydroxy pyrazole [3,4-d] pyrimidine A suspension of 3-amino pyrazole-4-carboxamide sulphate (10.4 grams) in 90 percent formic acid (l0.5 ml.) and formamide (25 ml.) was stirred and heated to 145 C. (At 1 C. complete solution is observed for a short period and thereafter a gradual precipitation occurs.) The reaction was held at 145 C. for 3 hours. The reaction mixture was then cooled to 5 C. and the product collected and washed with water (50 ml.) and acetone (2 X 50 ml.). Weight of crude product 6.2 grams. The crude product was recrystallized by dissolution in a solution made from sodium hydroxide (2.34 grams) in water (106 ml.) with treatment at 70 with charcoal (0.32 grams), followed by re-precipitation by the addition of concentrated hydrochloric acid to pH 5. The product was collected and washed with cold water (2 X 50 ml.) acetone (2 X 50 ml.) and dried in vacuo at 60 C. Weight= 5.8 grams. Yield 72 percent.

What is claimed:

1. A method of preparing the compound 3-amino-2- cyano acrylamide which comprises reacting formamidine base with cyanoacetamide at a temperature of less than about 30 C in the presence of water, lower alkanol, or a combination of both as a solvent therefore.

2. A method according to claim 1 in which the temperature is between 5 C to less than 30 C.

3. A method according to claim 2 in which the solvent is selected from the class consisting of water and lower alkanol.

4. A method according to claim 3 in which at least about equal molecular amounts of formamidine and cyanoacetamide are reacted together.

5. A method according to claim 2 in which at least about equal molecular amounts of formamidine and cyanoacetamide are reacted together. 

2. A method according to claim 1 in which the temperature is between 5* C to less than 30* C.
 3. A method according to claim 2 in which the solvent is selected from the class consisting of water and lower alkanol.
 4. A method according to claim 3 in which at least about equal molecular amounts of formamidine and cyanoacetamide are reacted together.
 5. A methOd according to claim 2 in which at least about equal molecular amounts of formamidine and cyanoacetamide are reacted together. 